Pathogenic species of bacteria come into contact with a variety of organisms in the environment and these interactions are important for their persistence, evolution and spread. Vibrio parahaemolyticus is a food-borne pathogen that causes gastroenteritis in humans. This bacterium naturally occupies various aquatic environmental niches in which it faces predation by various eukaryotic predators, including protozoa. The ability to survive in the environment in the presence of predation has significant environment and health consequences. Acanthamoeba castellanii is a model protozoan that has been shown to be a reservoir and/or vector for some species of pathogenic bacteria. V. parahaemolyticus is able to resist predation by A. castellanii and persist for more than 30 days in co-culture. This survival phenotype may play a role in the persistence of V. parahaemolyticus in the environment and the subsequent incidental spread to human hosts. In this application, A. castellanii will be used as a model to study the relationship between V. parahaemolyticus and free-living protozoa in the environment. A screen will be performed to understand, at the molecular level, the bacterial factors involved in survival in the presence of A. castellanii. In addition, the mechanism by which amoeba mediates the survival of V. parahaemolyticus will be examined. Together, these studies will provide a better understanding of the nature of the interaction between these two organisms and the consequence this has on V. parahaemolyticus as a pathogen. PUBLIC HEALTH RELEVANCE: Bacteria that cause disease have a lifestyle that involves survival in the environment. In this context, bacteria are subject to many pressures including predation by protozoa and other organisms. This application aims at understanding the mechanism by which Vibrio parahaemolyticus, a bacterium that seriously impacts the food industry and is the cause of worldwide outbreaks of food-borne illness, survives in the presence of environmental eukaryotic predators.